Breather bags are used in conjunction with sealed storage structures to balance the pressure differential between the atmosphere and the interior of the structure. Many configurations of breather bags are known and one of the most common is the semi-toroidal shaped bag. In a conventional system, one or more semi-toroidal shaped bags, fabricated with a curvature to complement the curvature of the storage structure, are mounted in the upper end of the structure adjacent the roof. Each bag is provided with a small diameter neck which is sealed within an opening in the roof of the structure so that the interior of the bag is exposed to atmospheric pressure, while the exterior of the bag is exposed to the pressure within the storage structure. The breather bag will expand and contract to compensate for pressure differentials between the atmosphere and the interior of the storage structure.
With the use of toroidal shaped bags, the breathing capacity is in large part determined by the diameter of the storage structure. Recently there has been a trend for taller storage structures and thus a greater breathing capacity is required than can be achieved by the normal toroidal shaped bags.
As the toroidal shaped bag is designed with a curvature to complement the curvature of the storage structure, it is necessary to inventory bags with different curvatures to accommodate different diameter structures. Furthermore, the toroidal shaped bag is fabricated by heat sealing a number of complexly shaped, plastic segments together. Because of the complexity of the configuration, the toroidal shaped bag is a relatively expensive item to manufacture.
During filling of the storage structure with a stored material, such as grain or silage, it is necessary to elevate the bag upwardly against the roof of the structure so that the bag will not interfere with the material as it is being fed into the structure. Secondly, it is important that the breather bag, when in its upper storage location, will not become entangled or entrapped with a free flowing stored material, such as grain. If the bag is entrapped with the grain, it can be sucked downwardly into the silo by the movement of the grain during unloading, which can cause a rupture in the bag and a loss of the hermetically sealed characteristics.
Because of this, there has been a need for a breather bag which can be readily withdrawn upwardly to a location so as not to interfere with the stored material as it is being introduced into the structure, and cannot become entangled with a free-flowing stored material.